Preparation of cyclopentadiene



Patented Mar. 23, 1948 Stanford J. Hetzel, Cheltenham, and Robert M.

" Kennedy, -Drexel Hill, Pa., assignors to Sun Oil Company,Philadelphia, Pa., a corporation of New Jersey No Drawing. ApplicationNovember 24, 1945, Serial u 630,692

This invention relates to 'cyclization. :Specifi cally it relates to:thedehydrogenation and Claims. (o1. 260-566) cyclization ofdehydrogenatable hydrocarbons,"

As stated, the invention is applicable 'tothe dehydrogenation andcyclization of pentane to 1,3 cyclopentadiene. This conversion isconsidered to take place by way of l-pentene and 1,3 pentadiene.Accordingly, the invention will be described with reference to theconversion of 1,3 pentadiene to 1,3 cyclopentadiene to which it ispre-eminently suited. These reactions can be represented as follows:

H Pentane 1 3 cyclopentadlene "having 5 carbon atoms per molecule,especially 1,3 pentadiene.- -More specifically the invention isconcerned with a'commercially feasible process for the conversion ofpentane or 1,3 pentadiene to1j3cyclopentadiene.

ously'effected at a temperature within, the range 300 Cato a temperatureat whi hs t nt composition of the hydrocarbons will take place. Morespecifically a temperature within the range 400C.-'700 0., preferably450 C.650 C., can

be employed: v r 7 While the conversion per pass'is substantiallyindependent of pressure; it has been found that lower pressures seemtoform'higher yields on recycling. Accordingly, while higher and lowerpressures are not excluded from the scope of the invention pressures inthe range of 1-00 mm. Hg-10 mm. Hg, preferably 200 mm. Hg-IO mm. Hg, canbe employed.

The time of contact of the 1,3 pentadiene with the chromic oxide onalumina is a factor to be considered. There is an optimum range ofcontact time corresponding to charging rates of 0.25 gram/minute/IOOgrams-10 grams/minute/IOO grams of chromic oxide on alumina. However,higher and lower charging rates are not excluded from the scope of theinvention.

Example 350 grams of 1,3 pentadiene were charged at a rate of 10grams/minute at a pressure of about 760 mm. Hg to 1000 grams of a mass,consisting of chromic (C1203) on alumina, in a conversion tube at atemperature of 600 C. The effluent from the conversion tube was cooled,condensed and fractionated resulting in a yield of 9.8 grams of 1,3cyclopentadiene. On recycle of the unconverted 1,3 pentadiene the yieldis 33 grams.

The contact mass employed was prepared by wetting alumina with chromiumnitrate, by immersing it therein. The alumina was then remove,d, dryedand ignited. Compositions containing from about 5% to about 35% CrzOs,by weight of the contact mass, preferably about 20%, can be employed.Compositions without this range are not excluded from the scope of theinvention, althoughthese are not now preferred.

The alumina employed was that commonly used in catalytic work; that is,it was in an activated state. Alumina in activated state can be preparedin several different manners all of which are well known in the art.

The contact mass can be regenerated indefinitely to substantially itsoriginal activity.

The particle or pellet size can be varied. About 4 to 8 mesh has beenfound quite satisfactory. Obviously the particle size should not be toosmall in the sense that a large pressure drop across the contact mass isto be avoided if substantially the same pressure in all parts of theapparatus is de- 7 3 sired, unless fluid or fluidized operation isemployed.

It will be apparent to those versed in the art that wide modificationand variation are possible within the scope of the invention as definedin the appended claims, the essence of the invention being in thatdehydrogenatable hydrocarbons having 5 carbon atoms per molecule can bedehydrogenated and cyclized by contacting the same at elevatedtemperature and suitable pressure with a mass consisting essentially ofchromic oxide onalumina as set forth herein and in the appended claims.

We claim: j

1. A process for the dehydrogenation and cyclization of 1,3 pentadieneto 1,3 cyclopentadiene which comprises contacting 1,3 pentadiene with amass consisting essentially of chromic' cyclization of 1,3 pentadiene to1,3 cyclopentadiene which comprises contacting 1,3 pentadiene with amass consisting essentially of chromic oxide on alumina at. atemperature within the range 400 C.700 C. for a time sufiicient toeffect a desired extent of conversion.

3. A process according to claim 2 wherein the pressure is in the range1000 mm. Hg-10 mm. Hg. 7

4. A process for the dehydrogenation and cyclization of 1,3 pentadieneto 1,3'cyclopentadiene which comprises contacting 1,3 pentadiene with amass consisting essentially of chromic oxide on alumina at a temperaturewithin the range 450 C.-650 C. at a pressure within the range 200 mm.Hg-10 mm. Hg for a time sufiicient to efiect a desired extent ofconversion.

5. A process according to claim 4 wherein the charging rate of 1,3pentadiene to the contact mass is within the range 0.25-10 grams/minute/100 grams of the contact mass and wherein the contact mass consists ofabout 5% to about of chromic oxide by weight.

, STANFORD J. HETZEL. ROBERT M. KENNEDY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 7 Date Taylor et a1 June '11, 1946

